Effect of Four Maturity Stages of Timothy Hay on Its Chemical Composition, Nutrient Digestibility and Nutritive Value Index

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Abstract
Timothy (Phleum pratense) hay was harvested at four stages of maturity and fed to sheep in order to determine the effect of forage maturity on nutrient digestibility and overall feeding value as measured by the Nutritive Value Index. Each maturity stage was also analyzed chemically. With advancing maturity in timothy hay from the early-bloom through the post-bloom stages, a downward trend in protein, ether extract and ash content was accompanied by an upward trend in the content of crude fiber, cellulose and lignin. There was no evidence of a change in the content of nitrogen-free extract or in the gross energy value of timothy hay with advancing maturity. In general, there was a decrease in the apparent digestibility of all fractions of timothy hay with increasing maturity. The digestibility of gross energy and crude protein fell progressively through all maturity stages. The digestibility of dry matter, crude fiber, cellulose and nitrogen-free extract declined progressively to the full-bloom stage after which there was no significant change. Ether extract digestibility decreased only at the post-bloom stage. In vitro cellulose digestion decreased with each advancing maturity stage of timothy hay. As a result of substantial decreases in both the intake and energy digestibility of timothy hay through each maturity stage, its overall nutritional value, as measured by the Nutritive Value Index, was significantly decreased as maturity was approached.